1. Field of the Invention
The present invention relates to a multi-spectral infrared imaging system that provides real-time measurement of flare combustion efficiency, which would enable operators to adjust flare operating conditions to achieve higher efficiency. The multi-spectral infrared imaging system includes a machine readable storage medium, which provides instructions that cause the multi-spectral infrared imaging system to perform operations to obtain a combustion efficiency of a flare.
2. Description of the Related Art
Flares are widely used in chemical process industries (e.g., petroleum refineries, chemical plants, etc.). Due to the intended function and nature of flare design and operations, determination of flare combustion efficiency (CE) and destruction and removal efficiency (DRE) is extremely challenging. There has been a protracted debate on how much air pollutants are emitted from flares. The fact is that no one has a good answer to this question and this level of uncertainty regarding flare emissions is problematic for both regulators and industry.
In 2010, Texas Commission on Environmental Quality (TCEQ) contracted University of Texas at Austin (UT) to conduct a comprehensive study on flare CE and DRE. The field work was conducted at John Zink facility in Tulsa, Okla. The results were reported in “2010 TCEQ Flare Study Project Final Report,” written by David T. Allen and Vincent M. Tones, on May 23, 2011. The results from this study were very valuable in characterizing flare CE and DRE, and had a lasting impact on flare operations and emission management. It should be noted that the study was successful in characterizing flare efficiency under the specific conditions targeted by the experiment design, however it did not cover flare operations under upset or emergency conditions, hydrogen flares, or flares specifically designed for routinely low flow applications.
The TCEQ-UT flare study was a major undertaking. The method used in this study could be referred to as “grab and measure” or “extractive sampling” method. However, it is not practical to use the same approach to measure or monitor flare operations on a regular basis. The TCEQ-UT study did include two supplemental remote sensing based measurement systems with an intention to evaluate their effectiveness for practical flare monitoring. The two systems were an infrared (IR) Hyper-Spectral Imager by Telops Inc. (Hyper-Cam) and a passive and active Fourier transform infrared (PFTIR and AFTIR, respectively, or FTIR for either) spectroscopy by Industrial Monitor and Control Corporation (IMACC).
The study results suggested that the flare CE determined by IMACC's PFTIR/AFTIR was generally consistent with the CE determined by analysis of pre- and post-combustion gas samples thru the “grab and measure” method. The mean differences between the two methods were about 2% to 2.5%, and average standard deviations were 2.8% to 3.2%. The data availability was 99% to 100%. The performance of Telops's Hyper-Spectral Imager was less desirable. The mean differences were 19.9%, standard deviations were 57.8%, and data availability was 39%.
Both the Telops's Hyper-Spectral Imager and the IMACC's FTIR are powerful instruments for many applications, particularly research projects. However, they have some significant shortcomings if they are to be used as industrial analyzers to determine flare CE. These shortcomings are identified below.
Fundamental/Technical Issues:
Telops' Hyper-Cam can be considered a two-dimensional array of FTIR spectrometers that can be combined to form images (i.e., each pixel in the image is equivalent to a single FTIR spectrometer). It has a scan rate of approximately 1 second per scan (depending on spectral resolution and other parameter settings). The flare plume changes rapidly in shape and position, and the resulting path length of the pixels in the Hyper-Cam Imager may change dramatically within the same data cube. This variability introduces unknown and uncontrollable factors into the pixel intensity-concentration equation, rendering calculations and results unreliable.
IMACC's FTIR is a path measurement instrument. The results only represent the region where the IR light path intersects the flare plume. Due to the heterogeneous and dynamic nature of a flare, using the measurement from a small path to represent the entire flare is a concern. The IMACC FTIR also has a relatively long scan time (seconds) and suffers the same problem as the Telops Hyper-Cam. Since the IMACC FTIR is a single-path measurement instrument, this variability can be minimized by pointing the instrument to the middle, thick portion of the flare plume where the relative change in path length is small. If the IMACC FTIR is aimed at the fringe of the flare plume, or if the flare diameter is small, the effect of this temporal mismatch due to flare plume dynamics is expected to be much more salient and problematic. Selection and alignment of the measurement path could significantly influence results. This makes it impractical for routine monitoring as the system would need some sort of targeting system to ensure it is consistently aimed at the correct position in the flare plume while the plume may be constantly shifting in wind.
Practical/Implementation Issues:
Both the Telops's Hyper-Cam and the IMACC FTIR are delicate research instruments and require expert-level personnel to operate. They require significant effort to set up and maintain, and significant effort is required for post-processing/analyzing data in order to derive flare CE results. They do not provide real-time or near real-time measurements, and are not suitable instruments to provide continuous real-time feedback to operational personnel. The total ownership cost is very high (this is particularly true for Telops' Hyper-Cam).
Flare emissions can swing over a wide range depending on operating conditions (e.g., amount of steam used to assist the flare). The current problem is that there is no mechanism to measure flare efficiency and provide timely feedback to flare operators to adjust operating conditions for a higher efficiency.